A little help please

[Anne]

I have a 2005 600f, I bought it a couple years ago and had to basically rebuild the poor beast. She is really a nice bike now. I have a small issue that I can't seem to figure out...when I get up to 80km/h I start hearing this rattle almost like a bicycle chain when you change gears. The faster you go the faster the rattle, when you drop under 80 it stops.
I have checked my chain and sprockets for wear and proper tension, checked the chain guide its has no wear marks. Any ideas would be greatly appreciated.
Thanks